Method and system for injecting slurry using concentrated slurry pressurization

ABSTRACT

A slurry injection system having a plurality of clear fluid pumps receiving clear fluid from a low pressure clear fluid manifold and pressurizing the clear fluid into high pressure clear fluid and communicating the high pressure clear fluid into the high pressure clear fluid manifold. A blender unit having low pressure slurry therein. A mixer receives clear fluid through a first valve. A slurry pressurizer in fluid communication with the high pressure clear fluid manifold through a second valve. The slurry pressurizer forms high pressure slurry by pressurizing the low pressure slurry from the blender unit using high pressure manifold clear fluid that is communicated to the mixer and communicates low pressure fluid to the low pressure clear fluid manifold. The mixer mixes the high pressure slurry and clear fluid from the first valve to form a mixture that is communicated to a slurry injection site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application of provisionalapplication 62/457,447, filed Feb. 10, 2017, the disclosure of which isincorporated by reference herein. This application also relates to USapplication entitled “Method and System for Injecting Slurry Using OneSlurry Pressurizing Tank” (Attorney Docket No. 9269C-000008-US) and USapplication entitled “Method and System for Injecting Slurry Using TwoCooperating Slurry Pressurizing Tanks” (Attorney Docket No.9269C-000009-US), filed concurrently herewith.

TECHNICAL FIELD

The present disclosure relates generally to a slurry injection system,and, more specifically, to a method and system for pressurizingconcentrated slurry for use in a continuous injection process.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Pumping of process fluids are used in many industries Process fluids maybe pumped with various types of pumps such as centrifugal, positivedisplacement or use of a pressurized drive fluid acting upon the processfluid. A slurry is one type of process fluid used in a process. Slurriesare typically abrasive in nature. Slurry pumps are used in manyindustries to provide the slurry into the process. Sand injection forhydraulic fracturing (fracking), high pressure coal slurry pipelines,mining, mineral processing, aggregate processing, and power generationall use slurry pumps. All of these industries are extremely costcompetitive. A slurry pump must be reliable and durable to reduce theamount of down time for the various processes.

Hydraulic fracturing of gas and oil bearing formations requires highpressures typically up to 15,000 psi (103421 kPa) with flow rates up to500 gallons per minute (1892 liters per minute). The total flow rateusing multiple pumps may exceed 5,000 gallons per minute (18927 litersper minute).

Slurry pumps are subject to severe wear because of the abrasive natureof the slurry. Typically, slurry pumps display poor reliability, andtherefore must be repaired or replaced often. This increases the overallprocess costs. It is desirable to reduce the overall process costs andincrease the reliability of a slurry pump.

Other components of the slurry injection system also have weaknesses dueto the abrasive slurries travelling therethrough. Check valves, rapidchanges in pressure, erosion or “wire drawing” caused by high velocityfluid and pipe joints themselves all are subject to failure. Further,pressure vessels are used and if a large number of penetrations in thetanks are used, those places are also subject to cracking failure.

SUMMARY

The present disclosure is directed to a method and system that allowsabrasive slurries to be injected into a very high-pressure processstream with minimal wear on the system components. The system provideshigh reliability due to the reduced amount of wear.

In one aspect of the disclosure, a slurry injection system comprises alow pressure clear fluid manifold, a high pressure clear fluid manifoldand a plurality of clear fluid pumps receiving clear fluid from the lowpressure manifold. The plurality of clear fluid pumps pressurize theclear fluid into high pressure clear fluid and communicates the highpressure clear fluid into the high pressure clear fluid manifold. Thesystem further includes a blender unit having low pressure slurrytherein and a mixer in fluid communication with the high pressure clearfluid manifold through a first valve. A slurry pressurizer is in fluidcommunication with the high pressure clear fluid manifold through asecond valve, the mixer, the blender unit and the low pressure clearfluid manifold. The slurry pressurizer forms high pressure slurry bypressurizing the low pressure slurry from the blender unit using highpressure clear fluid from the high pressure clear fluid manifold. Theslurry pressurizer communicates high pressure slurry to the mixer andcommunicating low pressure fluid to the low pressure clear fluidmanifold. The mixer mixes the high pressure slurry and clear fluid fromthe first valve to form a mixture that is communicated to an injectionsite.

In another aspect of the disclosure, a method of operating a slurryinjection system comprising a low pressure clear fluid manifold, a highpressure clear fluid manifold, a plurality of clear fluid pumps, ablender unit, a mixer, and a slurry pressurizer comprises receivingclear fluid from the low pressure clear fluid manifold at the pluralityof clear fluid pumps, pressurizing the clear fluid into high pressureclear fluid at the plurality of clear fluid pumps, communicating thehigh pressure clear fluid into the high pressure clear fluid manifoldfrom the plurality of clear fluid pumps, communicating high pressureclear fluid from the high pressure clear fluid manifold to the mixerthrough a first valve, communicating the high pressure clear fluid fromthe high pressure clear fluid manifold to the slurry pressurizer througha second valve, pressurizing, by the slurry pressurizer, low pressureslurry from the blender unit using high pressure clear fluid from thehigh pressure clear fluid manifold to form high pressure slurry,communicating low pressure fluid from the slurry pressurizer to the lowpressure clear fluid manifold, blending, at a mixer, the high pressureslurry with high pressure clear fluid from the second valve to form aslurry mixture, and communicating the mixture to an injection site.

In another aspect of the disclosure, a system for injecting slurry froma slurry source into a slurry injection site comprises a first elongatedtank comprising a first end having a first volume and a second endhaving a second volume, said first volume separated from the secondvolume, a first pipe having a first end external to the first elongatedtank receiving clear fluid and a second end coupled to the first volumeand a plurality of slurry valves fluidically coupled to the firstelongated tank. The plurality of slurry valves have a first statecommunicating high pressure slurry from the second volume to the slurryinjection site and a second state communicating low pressure slurry intothe second volume. A plurality of clear fluid valves are fluidicallycoupled to the first elongated tank and communicate high pressure clearfluid to the first volume in the first state and communicate lowpressure clear fluid from the first volume in the second state.

In yet another aspect of the disclosure, a method of injecting slurry ata slurry injection site using a slurry injection system having a firstelongated tank having a first volume and a second volume comprises usinga plurality of slurry valves fluidically coupled to the first elongatedtank. The method further comprises in a first state, communicating highpressure slurry from the second volume to the slurry injection site andin a second state, communicating low pressure slurry to the secondvolume. The method further comprises using a plurality of clear fluidvalves fluidically coupled to the first elongated tank, in a firststate, communicating high pressure clear fluid to the first volume, and,in a second state, communicating low pressure clear fluid from the firstvolume.

In yet another aspect of the disclosure, a system for injecting slurryfrom a slurry source into a slurry injection site includes a firstelongated tank comprising a first end having a first volume and a secondend having a second volume, said first volume separated from the secondvolume. The system further includes a first pipe having a first endexternal to the first elongated tank receiving clear fluid and a secondend coupled to the first volume. The system further includes a secondelongated tank comprising a first end having a third volume and a secondend having a fourth volume, said third volume separated from the fourthvolume. The second elongated tank has a second pipe having a first endexternal to the second elongated tank that receives clear fluid and asecond end within the third volume. A plurality of slurry valvesfluidically are coupled the first elongated tank and the secondelongated tank. The plurality of slurry valves have a first statecommunicating high pressure slurry from the second volume to the slurryinjection site and communicating low pressure slurry to the fourthvolume and a second state communicating low pressure slurry to thesecond volume and high pressure slurry from the fourth volume to theslurry injection site. A plurality of clear fluid valves are fluidicallycoupled to the first elongated tank and the second elongated tank andcommunicate high pressure clear fluid to the first volume andcommunicate low pressure clear fluid from the third volume in a firststate and communicating low pressure clear fluid to the first volume andhigh pressure clear fluid to the third volume in a second state.

In a further aspect of the disclosure, a method of injecting slurry at aslurry injection site using a slurry injection system having a firstelongated tank having a first volume and a second volume and a secondelongated tank having a third volume and a fourth volume comprisingusing a plurality of slurry valves fluidically coupled to the firstelongated tank and the second elongated tank. in a first state,communicating high pressure slurry from the second volume to the slurryinjection site, and communicating low pressure slurry to the fourthvolume. In a second state, communicating low pressure slurry to thesecond volume, and communicating high pressure slurry from the fourthvolume to the slurry injection site. Using a plurality of clear fluidvalves fluidically coupled to the first elongated tank and the secondelongated tank, in a first state, communicating high pressure clearfluid to the first volume, and communicating low pressure clear fluidfrom the third volume in a first state and, in a second state,communicating low pressure clear fluid to the first volume, andcommunicating high pressure clear fluid to the third volume.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1A is a schematic view of a slurry injection system according to afirst example of the present disclosure.

FIG. 1B is a schematic view of a slurry injection system according to asecond example of the present disclosure.

FIG. 1C is a side view of a horizontally disposed tank for use in theslurry injection system.

FIG. 1D is a side view of an alternative configuration of a tankdisposed horizontally.

FIG. 1E is a cross-sectional view of the tank of FIG. 1D.

FIG. 1F is an alternative cross-sectional view of the tank of FIG. 1D.

FIG. 1G is a schematic view of a slurry injection system according to athird example of the present disclosure.

FIG. 1H is a cross-sectional view of a piston formed according to theexample of FIG. 1G.

FIG. 1I is a schematic of a first example of a one tank system with highpressure clear fluid depressurization.

FIG. 1J is a schematic of a second example of a one tank system withouthigh pressure clear fluid depressurization.

FIG. 2A is a cross-section of an exemplary three-way valve in a firstposition.

FIG. 2B is a cross-section of the exemplary three-way valve in a secondposition.

FIG. 3A is a second example of an exemplary three-way valve in a firstposition.

FIG. 3B is a second example of the exemplary three-way valve in a secondposition.

FIG. 3C is a cross-section of a first example of a two-way switch.

FIG. 3D is a cross-section of a second example of two two-way switcheshaving two housings and a common actuator in a first position.

FIG. 3E is a cross-section of the second example of the two two-wayswitches of FIG. 3D in a second position.

FIG. 3F is a cross-section of a third example of a two-way switch.

FIG. 3G is a cross-section of a fourth example of two two-way switcheshaving two housings with a common actuator in a first position.

FIG. 3H is a cross-section of a fifth example of the two-way switches ofFIG. 3G in a second position.

FIG. 4A is a first example of a table for the various valve settingsused during operation of the example of FIG. 1A.

FIG. 4B is a second example of a table for the various valve settingsused during the operation of the example illustrated in FIG. 1B.

FIG. 4C is a third example of a table for the various valve settingscorresponding to FIG. 1E.

FIG. 5 is a flowchart for a first example of a method for operating thesystem.

FIG. 6 is a flowchart of a method for switching states between a firsttank and a second tank injection slurry.

FIG. 7A is a timing chart of an injection system for a multiple unitslurry injection system with a dwell time.

FIG. 7B is a timing chart of the injection system for a multiple unitslurry injection system with no dwell time.

FIG. 8A is a schematic of a slurry injection system disposed ontrailers.

FIG. 8B is an enlarged cross-sectional view of the static mixer of FIG.8A.

FIG. 9 is a flowchart of a method for operating the system of FIG. 8.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Forpurposes of clarity, the same reference numbers will be used in thedrawings to identify similar elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical or. It should be understood thatsteps within a method may be executed in different order withoutaltering the principles of the present disclosure. The use of the words“low” and “high” are used relative to the pressures suitable for use infracking. “Low” pressure is suitable for movement of fluids into or outof pipes. “High” pressure is on the order suitable for fracking which istypically thousands of pounds per square inch.

A slurry injection system 10 is illustrated for injecting slurry into ahigh pressure injection site 12. The injection system 10 may be usedalone or in a multi-unit injection system such as the injection systemunit 10A illustrated in fluid communication with the injection site 12.The injection systems 10, 10A may be operated using a common controller20 such as a programmable logic controller (PLC). The controller 20 maybe used to control the plurality of valves within the injection system10 and the injection system 10A based on feedback from sensors such asflow rate sensors 22, 24. The flow rate sensors 22, 24 generate a firstflow rate signal and a second flow rate signal.

The injection system 10 is used for injecting slurry from a slurrysource such as a slurry tank 30 using a slurry circulation pump 32. Theslurry, under low pressure from the circulation pump 32, is communicatedto a first tank 40A and a second tank 40B through a low pressure slurryinlet pipe 34. As set forth below, the low pressure slurry iscommunicated to one tank at a time.

The first tank 40A and the second tank 40B may be cylindrical orelongated in shape and disposed in a vertical or any angle abovehorizontal manner as is illustrated. As will also be described below, itmay be possible that the tanks may be positioned in a horizontalposition. The tanks 40A, 40B have respective vertical longitudinal axes42A, 42B, respectively. The tanks 40A, 40B each have a respective endcap 44A, 44B. The tanks 40A, 40B have respective first ends 46A, 46B andsecond ends 48A, 48B. The first end 46A of the first tank 40A has afirst volume 50 of clear fluid and the second end 48A of the first tank40A has a second volume 52 of slurry. The second tank 40B has a thirdvolume 54 of clear fluid at the second end 46B and a fourth volume 56 ofslurry at the second end 48B. The volumes 50, 52, 54 and 56 vary duringthe process.

The tanks 40A, 40B each include a longitudinally extending pipe 60A,60B. The pipes 60A, 60B may be coaxial with the longitudinal axes at42A, 42B. Each pipe 60A, 60B may extend from outside of the respectiveend caps 44A, 44B through an opening 62A, 62B. The pipes 60A, 60B extendto the first ends 46A, 46B through the second ends 48A, 46B of the tanks40A, 40B.

A flow distribution plate 64A, 64B may be disposed at the ends of thepipes 60A, 60B toward the first ends 46A, 46B of the tanks 40A, 40B. Theflow distribution plates 64A, 64B distribute incoming clear fluid acrossthe diameter of the tanks to minimize the mixing of clear fluid with theslurry.

Each tank 40A, 40B is separated by a separation region 68A, 68B. Whilethe region may be a defined area, in a hydraulic fracturingconfiguration, clear fluid may be separated from slurry naturally due tothe less dense nature of the clear fluid. Should some mixing occur, theconcentration of the slurry may be compensated for this. In thisexample, the clear fluid is disposed at the first ends 46A, 46B of thetanks 40A, 40B. The slurry is disposed at the second ends 48A, 48B. Theclear fluid may be water, water mixed with chemicals or slurry additivessuch as ethylene glycol or other types of hydraulic fluid. “Clear”, inthis manner, refers to fluid that does not contain the particles of theslurry.

The slurry may contain various types or sizes of sand particles such assmall quartz particles. The slurry may also include other types ofchemicals to improve the lubrication and movement of the hydraulicfracturing particles therein.

The end caps 44A, 44B are affixed to the tanks 40A, 40B and may includeconical portions 70A, 70B, respectively. The conical portions 70A, 70Bmay have a larger diameter toward the second volumes 42, 56 and taper toa smaller diameter at the bottom or outer end of the end caps 44A, 44B(longitudinally away from the second volumes 42, 56). The end caps 44A,44B may also include cylindrical portions 72A, 72B that are coupled to aplurality of slurry valves. The plurality of slurry valves may includeoutlet valves 80A, 80B and inlet valves 82A, 82B. Valves 80A, 80B areused for communicating slurry under high pressure from the tanks 40A,40B, respectively. In operation, the valves 80A, 80B may alternatelycommunicate slurry from the second ends 48A, 48B of the respective tanks40A, 40B.

Inlet valves 82A, 82B communicate fluid from the slurry inlet pipe 34into the respective tanks 40A, 40B. The inlet valves 82A, 82B mayoperate alternately so that each of the valves 82A, 82B does not operateat the same time.

The valves 80A through 82B may be check valves that operate in themanner described below. That is, in general, one tank is receiving highpressure clear fluid to force high pressure slurry from the tank whilethe other tank is receiving low pressure slurry and removing lowpressure clear fluid therefrom.

The injection site 12 has an injection manifold 94 that is incommunication with a pipe 96 that extends from the check valve 80A and apipe 98 that extends from the check valve 80B.

A plurality of clear fluid valves are used for communicating clear fluidto and from each of the tanks 40A, 40B and are in fluid communicationwith a high-pressure clear fluid pump 90 and a clear fluid tank 92.

The clear fluid tank 92 supplies clear fluid to the high-pressure pump90 through pipe 100 and the flow rate sensor 24. A pipe 102 suppliespressurized clear fluid to a three-way valve 110. The three-way valve110 has an inlet port 110A, a first outlet port 110B and an outlet port110C. A pipe 112 fluidically communicates fluid from the outlet port110C to the injection manifold 94 (or pipe 96 which leads to theinjection manifold 94). A pipe 114 communicates high pressure clearfluid from the outlet port 110B to a second three-way valve 120. Thevalves 110 and 120 may be referred to as high pressure valves. A bypassvalve 124 may also communicate fluid from the high pressure pump 90 tothe pipe 114 through pipe 126. The valve 124 may be a two-way valve usedto controllably pressurize port 110B and pipe 114 during changingstates. The operation of valve 124 will be described in further detailbelow. The three-way valve 110 communicates fluid from the inlet port110A to either the outlet port 110B or the outlet port 110C undercontrol of the controller 20.

The three-way valve 120 selectively communicates high pressure clearfluid from the inlet port 120A to either the first outlet port 120B orthe second outlet port 120C. Outlet port 120B is in fluid communicationwith the pipe 60A through pipe 128. Outlet port 120C is in fluidcommunication with the pipe 60B through pipe 130. Valve 120 is undercontrol of the controller 20.

A three-way valve 140 is used for selectively communicating low pressureclear fluid from the tanks 40A and 40B under control of the controller20. In particular, valve 140 has an inlet port 140A in fluidcommunication with pipe 60A through pipe 142. The valve 140 also has aninlet port 140B in fluid communication with pipe 60B through pipe 144.An outlet port 140C of valve 140 is in fluid communication with theclear fluid tank 92. The fluid from the outlet port 140C is in fluidcommunication with the flow rate sensor 22 and a two-way flow controlvalve 146. Both the valves 140 and 146 are controlled by the controller20. The amount of fluid communicated to the tank 92 may be controlled byselectively controlling the amount of fluid flowing through the valve146. The fluid communicated through the valves 140 and 146 is under lowpressure as will be described in further detail below. The closed inletport 140A or 140B of valve 140 is under high pressure due to the highpressure slurry operation. A pipe 148 communicates fluid from the valve146 to the tank 92.

A three-way valve 150 is also in communication with the tanks 40A and40B. In particular, the valve 150 includes an inlet port 150A in fluidcommunication with the pipe 60A through pipe 152. Inlet port 150B is influid communication with the pipe 60B through pipe 154. Outlet port 150Cof valve 150 is in fluid communication with the pipe 148 through pipe156. The valve 150, as will be described in more detail below, is usedfor equalization or reduction of the pressure within the tanks 40A, 40B.The valve 150 is used for communicating clear fluid from the firstvolume 50 and the third volume 54. The valve 150 selectivelycommunicates high pressure clear fluid from either the inlet port 150Aor port 150B to the outlet port 150C which ultimately communicates clearfluid through the pipe 156 to the tank 92. The pipe 156 may be directlyinput into the tank 92 or fluidically coupled to pipe 14B. The valve 150is used to lower the pressure within the highly pressurized tanks priorto when the state of the valves 110, 120 is changed. Ultimately, the useof the valve 150 helps reduce the overall pressure and thus the effortto switch valves 110 and 120 is lower and potential for valve wear anderosion is reduced.

Pipes 60A and 60B may also be in fluid communication with a respectivevalve 160A, 160B. The valves 160A and 160B are at the lowest point ofthe respective pipes 60A, 60B and are used to purge air from the volumewithin the respective 40A, 40B.

A check valve 170 may also be in communication between the injectionmanifold 94 and the pump 90. In the illustration, check valve 170 isfluidly coupled between the pipe 102 and the injection manifold 94. Thecheck valve 170 is used for directing the flow from the high pressurepump 90 to the injection manifold during upset conditions such as whenthe fluid paths, the high pressure valves or pipes associated therewithbecome blocked or equipment, such as the valves, fail. The check valve170 may also include a spring 172. The spring 172 keeps check valve 170closed until the upstream pressure (at the pipe 102) exceeds thedownstream pressure (in the pipe 96) by a certain amount.

The valves 110 and 120 may be referred to as high pressure clear fluidvalves. Valve 124 may also be included as a high pressure clear fluidvalve. Valves 140 and 146 may be referred to as low pressure clear fluidvalves. The valve 150 sees a combination of high pressure at the inletports 150A, 150B and low pressure at the outlet port 150C. The valve 124is used for pressurizing the pipe 114 at a certain rate with highpressure clear fluid as will be described in more detail below.Collectively, the valves 110, 120, 124, 140 and 146 may be referred toas clear fluid valves. The plurality of clear fluid valves communicatesboth high pressure and low pressure fluid to and from the tanks 40A and40B.

The valves 110, 120 and 140 are capable of handling extreme highpressures such as 15,000 psi (103421 kPa) at flow rates at hundreds ofgallons per minute to provide such sealing force over 50,000 pounds(344737 kPa) may be provided against the valve seat. An extremely highdifferential is present. However, the valve 150 may be used to lower theoverall pressure during switching. The purpose of valve 110 is toisolate the system by diverting the high-pressure clear fluid flow tothe slurry line 96 through pipe 112. After system isolation, valve 150can bleed of residual high pressure thereby placing components of thesystem at relatively low pressure. The operation of the valves will bedescribed in more detail below. Although the valves are described as“three-way valves” and “two-way valves” and “check valves”, other typesof valves may be substituted therein. The three-way valves may beimplemented in a plurality of two-way valves. Of course, other types ofvalves may be substituted from the valves. Check valves may, forexample, be two-way valves controlled by the controller 20.

The valves 110, 120, 124, 140, 146 and 150 may be controlled by thecontroller 20 through the use of electrical signals therefrom. Othervalves such as 160A and 160B, although not illustrated in communicationwith the controller 20, may also be electrically controlled thereby. Inaddition to electrically, valves 110, 120, 124, 140, 146, 150, 160A and160B may also operate hydraulically or pneumatically

Referring now to FIG. 1B, an injection system 10′ is illustrated andlabeled identically to that of FIG. 1A. The system 10′ illustrated inFIG. 1B operates identically to that set forth in FIG. 1A and may alsobe part of a multi-unit system. The difference between the systems 10and 10′ is the three-way valve 150 has been replaced by a pair oftwo-way valves 210A and 210B for pressure reduction. The two-way valves210A, 210B are used for communicating high pressure clear fluid to theclear fluid tank 92. The pipe 152 receives clear fluid from the pipe 60Awhich in turn is communicated through pipe 156 to the clear fluid tank92. The valve 210B receives clear fluid from the pipe 60B through pipe154. The valve 210B communicates clear fluid through the pipe 156 to theclear tank. For simplicity in overall maintenance and the like, thetwo-way valves 210A and 210 B may be identical to that of valve 124.That way, maintenance is made easier due to the commonality of parts.The valves 210A and 210B all operate at a high differential and thus mayneed to be serviced more than the other valves in the system whichoperate with low pressure differentials between the inputs and theoutputs.

The valves 210A and 210B are in electrical communication with thecontroller 20. That is, the controller 20 may control the opening andclosing of the valves 210A, 210B. As will be described in more detailbelow, the valves may be operated so that either 210A or 210B are openbut not both.

Referring now to FIG. 1C, the tank 40A is disposed vertically. The samereference numerals set forth in FIGS. 1A and 1B are used in FIG. 1C.Because of the higher density of slurry within the tank 40A, the denserslurry will settle toward the bottom of the tank 40A. This results inthe clear fluid therein pushing a greater amount of fluid near the toprelative to the bottom of the tank in the horizontal direction. As isillustrated, the interface 68A′ is generally at an angle where the topportion is closer to the endcap 44A.

Referring now to FIG. 1D, an alternative embodiment of the horizontaltank 40A is set forth. In this example, a plurality of partitions 180are used to define a plurality of horizontal channels 182. Thepartitions 180 help reduce the amount of departure of the interface 68A″from vertical. In this example, the partitions 180 are formed with aplurality of types that extend in the longitudinal direction. The pipesin this example are cylindrical in shape and have gaps 184 therebetween.The gaps 184 also define horizontal channels within the tank 40A.

In FIG. 1D, the endcap 44A′ is modified to have an enlarged conicalportion 70A′. The conical portion 70A′ extends in a vertical directionso as to be in fluid communication with the horizontal channels 182.That is, the diameter of the conical portion 70A′ adjacent to thechannels 182 has been increased. Thus, the conical portion 70A′redirects slurry both to and from the check valves 82A and 82B.

Referring now to FIG. 1E, a cross-sectional view of one example of thetank 40A is set forth. As can be seen, gaps 184 are disposed between thepartitions 180 so that horizontal channels 182 are formed. Thepartitions are cylindrical in shape and may be formed by pipes. The pipe60A provides clear fluid to the distributor plate 64A and distributesthe clear fluid through the channels 182 and gaps 184 formed by thepartitions 180.

Referring now to FIG. 1F, a plurality of partitions are illustratedhaving radially extending walls 190 that extend from the pipe 60A to theinner wall of the tank 40A. The walls 190 divide the tank intopie-shaped sectors 192. The pie-shaped sectors 192 may be furtherdivided by a concentric wall 194. The concentric wall 194 shares acenter point with the tank 40A and the pipe 60A. The walls 190, 194 actas a partition to reduce the amount of displacement of the slurry in anangular manner as illustrated in FIG. 1D.

Referring now to FIGS. 1G and 1H, a slurry injection system 10″ has eachof the tanks 40A and 40B with a physical divider between the clear fluidbetween the first volume 50 and the second volume 52 and between thethird volume 54 and the fourth volume 56 rather than the regions 68A,68B described above. The tank 40A may be disposed horizontally (FIGS. 1Aand B), vertically (FIGS. 1C-F) or at angles therebetween. The physicaldivider may be a piston 220A that has a first opening 222 for receivingthe pipe 60A. A piston 220B configured in the same manner may be used intank 40B around pipe 60B. The piston 220A is loosely fit around the pipeso that the piston 220A can freely travel along the pipe 60A as thepressure of the clear fluid changes. By providing the piston 220A, amore complete separation of the clear fluid and the slurry is providedwith less chance of mixing with the slurry. With very high fill anddischarge rates, some turbulence may occur and the slurry may mix withthe fluid in the configuration of FIGS. 1A and 1B. Further, the tanks40A, 40B may be oriented in a horizontal position. Providing pistons220A, 220B also enables the use of the tanks in a horizontal to preventthe mixing of the different fluids within the tank. In tank 40A, thepiston 220A is shown in a first position and dotted in a secondposition. Thus, the piston 220A may move in a longitudinal directionparallel to the longitudinal axis of the tank.

When the piston 220A reaches the end cap 44A, a flap 230 disposed withinan opening 232 may open by rotating at the hinge 234. The flap 230 maybe a spring-loaded flap and when a sufficient amount of pressuredifferential is formed between the two sides of the piston 220A, theflap 230 may provide some clear fluid through the opening 232. The hinge234 may instead be spring-loaded to provide a resistance from the flap230 opening until the piston 220 reaches the end cap 44A of the tank40A. The dotted flap illustrates the open position of the flap 230. Itmay be desirable to allow a small amount of clear fluid from volume 50to travel through the conical portion 70A into the cylindrical portion72A and into opening 62A of the end cap 44A so that the clear fluidflows just past check valve 80A and into the pipe 96. The conical shapeminimizes flow turbulence of the slurry out of the tanks 40A, 40B. Thisallows the check valve 80A to close within clear fluid and thus in acleaner environment. Tank 40B may also be operated in a similar mannerin that the clear fluid may transmit through the piston 220B so that thecheck valve 80B closes in a cleaner environment. The force needed toopen the flap 230 by overcoming the spring force may be relativelysmall. That is, only a few pounds per square inch may be sufficient toopen the flap to allow the fluid to flush the check valves 80A or 80B.

Referring now to FIG. 1E, the same reference numerals are used toindicate the same components as FIGS. 1A-1D. In this example, only asingle tank 40A is provided with the attached components in the slurryinjection 10′″. In this example, the tank 40A may be configured in thesame manner as set forth in FIG. 1A or 1G in that the separation region68A or the piston 220A (of FIGS. 1G and 1H) may be set forth between thefirst volume 50 and the second volume 52.

One difference between FIGS. 1A-1H and FIG. 1I is the lack of a slurrytank 30 and pump 32. In this example, the check valve 82A is in fluidcommunication with a low pressure slurry manifold 240. The low pressureslurry manifold 240 may be a common source shared between multiple tanksin a multiple tank type system. Of course, a slurry tank 30 and pump 32may be in communication with the low pressure slurry manifold 240.Another difference between FIG. 1E and FIGS. 1A-1H is the lack of a highpressure pump 90 and a low pressure fluid tank 92. A low pressure clearfluid manifold 242 is used to receive the low pressure fluid from theport 140A′. A high pressure clear fluid manifold 244 is in communicationwith the valve 110. Although the pump 90 is not illustrated in thisexample, a high pressure clear fluid pump may be used somewhere in thesystem for generating the high pressure within the high pressure clearfluid manifold 244.

In this example, the flow rate sensor 24′ has been modified to bepositioned downstream of the valve 110 rather than between the clearfluid tank and the pump as illustrated above. The flow rate sensor hasbeen labeled 24′ to indicate its change of position. However, the flowrate sensor 24′ generates a flow signal corresponding to the amount offlow into the pipe 60A and thus into the tank 40A.

The valves 120 and 140 illustrated above have been changed fromthree-way valves to two-way valves and are indicated as valve 120′ and140′. Port 120B′ is in fluid communication with the pipe 60A. Likewise,port 140B′ is also in fluid communication with the pipe 60A. Port 120A′is in fluid communication with the flow rate sensor 24′, pipe 114 andvalve 124 and port 1106 of valve 110.

The slurry injection system^(IV) may be referred to as an asynchronoussystem. In the previous figures, the fill rate of given tank is nofaster than the discharge rate of the second tank. However, byincreasing the fill rate of the slurry, the slurry fill duration can besubstantially reduced and the higher capacity high pressure slurry foreach tank is increased.

In operation, the three-way valve 110 communicated fluid from port 110Athrough 1106. The high pressure fluid enters pipe 114 and flow ratesensor 24′. The valve 120′ communicates fluid from port 120A′ to 120B′and into the pipe 60A. It is presumed that the tank 40A was previouslyfilled with low pressure slurry. The high pressure clear fluid forceshigh pressure slurry through check valve 80A and to the injection site12 through the injection manifold 94. As in a similar manner to that setforth above, when the flow rate sensor 24′ indicates the volume of clearfluid has flushed the slurry from the tank 40A and, if desired, passedcheck valve 80A, the three-way valve 110 is commanded to divert fluidfrom port 110A to outlet port 110C. Valve 210A is open whichdepressurizes the pipe 60A and the tank 40A by communicating fluid tothe low pressure clear fluid manifold 242. Valve 120′ is closed andvalve 140′ is open under low pressure. Thereafter the valve 210 isclosed. Low pressure slurry from the low pressure slurry manifold 240opens the check valve 82A to allow low pressure slurry to enter the tank40A and expel clear fluid through the pipe 60A. The clear fluid leavesthe tank 40A and pipe 60A through the open valve 140′. The opening andclosing of the valves is under the control of the controller 20. Theflow rate sensor 22 is used to indirectly determine the amount of slurrythat has entered the tank 40A. When the amount of slurry as determinedby monitoring the flow of clear fluid out of the tank, valve 140′ isclosed and valve 120′ is open. The valve 124 is open which directs highpressure clear fluid from the high pressure clear fluid manifold 244 tobe communicated to the pipe 114 through the pipe 126. After somepressure is built up in pipe 114, valve 110 communicates high pressureclear fluid from port 110A to port 1106 and valve 124 is closed. Highpressure clear fluid then enters the pipe 60A through valve 120′ andcheck valve 82A is closed and check valve 80A is open.

The valve 170 is configured in a similar manner to that described aboverelative to the spring 172. That is, the valve 170 may also include aspring 172 in a similar manner to that set forth above. Valve 170 openswhen a sufficient force is between the high pressure clear fluidmanifold 244 and the pipe 96 or the injection site 12. Again, the valve170 is open when damage to the valve or other components of the systemis present or flow conditions have been upset. The valve 170 should beopen when the upstream pressure is about 100 pounds per square inchhigher than the downstream pressure. This ensures that the valve willnot open during normal operation.

Referring now to FIG. 1F, the same components set forth in FIG. 1E arelabeled in the same manner. In this example, the slurry injection system10 ^(IV) has valves 120′ and 140′ that are presumed to be robust enoughto be switched under high pressure. Thus, there is no pressure reliefusing valves 110 and 124 as in the previous examples. In this example,the flow rate sensor 24′ measures the amount of high pressure clearfluid that is communicated to the pipe 60A through the valve 120′. Valve140′ is closed. Clear fluid displaces slurry through the check valve80A. When the amount of slurry through the check valve 80A has reachedclear fluid as determined by the flow rate sensor 24′ and thus thevolume of fluid, the valve operation is reversed in that valve 120 isclosed while valve 140 is open. This allows the tank 40A to bedepressurized and low pressure slurry is then communicated to the tankto restart the process. When the amount of clear fluid that leaves thetank corresponds to a desired amount of slurry being input to checkvalve 80A, the valves 120′ and 140′ are reversed in operation.

Referring now to FIGS. 2A and 2B, a valve 250 suitable for use as valve110 or 120 in FIGS. 1A-1C is set forth. The valve 250 has a housing 252which may be cylindrical in shape. The housing 252 includes an inlet orcentral port 254, a first outlet port 256 and a second outlet port 258.A pair of valve seats 260, 262 extends from the interior cavity 264 ofthe housing 252. The valve seat 260 is disposed between the inlet port254 and the outlet port 258. The valve seat 262 is disposed between theinlet port 254 and the outlet port 256.

An actuator 270 has a spindle 272 which has a first valve disk 274 and asecond valve disk 276 fixable coupled thereto. The valve disk 274 isdisposed between the inlet port 254 and the valve seat 262. The valvedisk 276 is disposed between the inlet port 254 and the valve seat 260.Packing 280 may be disposed between the spindle 272 and the housing 252to facilitate longitudinal movement of the spindle 272 and the valvedisks 274 and 276 as in the direction illustrated by the arrows 282 andto prevent leakage of fluid from cavity 264. In FIG. 2A, the valve disks274, 276 and spindle 272 are moved in a longitudinally outward directionaway from the actuator 270 so that the fluid flows between the inletport 254 and the outlet port 258 as illustrated by the path 284. In FIG.2B, the spindle is moved in the rightmost position toward the actuator270 so that fluid travels from the inlet port 254 to the outlet port256.

The actuator 270 may be various types of actuators such as an electricalactuator or a hydraulic actuator. In this example, an electric actuatorhas been used. The actuator 270 is sized to move the disks 274, 276 sothat high pressure flow between the inlet port and one of the outletports is provided (once resumed during the state switching process).Further, the path corresponding to FIG. 1A is a high pressure clearfluid path of clear fluid. The other port which is closed is at a lowpressure. The low pressure port corresponds to tank 40A or 40B dependingon the state of operation. The high pressure input to the housing“pushes” the closed valve disk against the corresponding valve seat toensure a very high closing force to prevent leakage. Because the highpressures are relieved during the switching process, the actuator issized to overcome very little force (a little more than the packingplaces on the spindle 272).

Referring now to FIGS. 3A and 3B, a valve 250′ is illustrated having thesame reference numerals as FIGS. 2A and 2B except for the changedcomponents. The valve 250′ illustrated in FIGS. 3A and 3B is suitablefor use as valve 140 illustrated in FIGS. 1A-1C. In this example, thevalve seats 260 and 262 have been changed to valve seats 260′ and 262′.In this example, the valve seats 260′, 262′ are moved closer to thecentral port 290, which is an outlet port. The valve disks 274 and 276are moved outboard of the valve seats 260′ and 262′. In this example,the valve 250′ has one outlet port 290 and two inlet ports 292, 294. Oneof the inlet ports is at low pressure and one is at high pressure duringoperation. The open port is at low pressure. The high pressure on thevalve disk at high pressure forces it in communication with theassociated valve seat. For example, in FIG. 3A, valve disk 274 is forcedagainst valve seat 262′. In FIG. 3B, valve disk 276 is forced againstvalve seat 260′. In FIG. 3A, fluid path 296 communicates fluid from thesecond tank 40B to the outlet port 290 through fluid path 296. In FIG.3B, fluid is communicated from tank 40A to outlet port 290 through fluidpath 298. In each of the cases of FIGS. 2A-3B, a gap between the valvedisks and the valve seats allows fluid to pass therethrough.

Referring now to FIG. 3C, a two-way valve 310 may be used to replace thethree-way valves illustrated in FIGS. 1A-1F. That is, more than onetwo-way valve may be used to replace the three-way valves illustrated inthe example set forth above. For a two-tank operation, two two-wayvalves may be used to replace a three-way valve. The valve 310 may alsobe used in a one tank solution as valves 120′ or 140′. The valve 310includes a housing 312 that has an inlet port 314 and an outlet port316. The housing 312 includes packing 320 through which an actuator rod322 extends therethrough. The actuator rod 322 includes a valve disk 324which is moved by an actuator 326 coupled to the rod 322. The valve disk324 may be displaced against the valve seats 326. When the valve disk324 contacts the valve seat 326, the valve 310 is sealed and thus noflow from the inlet port 314 to the outlet port 316 takes place. In thisexample, when each of the three-way valves are replaced with two-wayvalves, each valve may have an independent actuator 326 to allowindependent control. Thus, each two-way valve may have greater freedomin valve timing.

Referring now to FIGS. 3D and 3E, a pair of two-way valves 310 areillustrated coupled to a common actuator 326. The common components ofeach valve are primed. In FIG. 3D, the right valve 310′ is open whilethe left valve 310 is closed. In FIG. 3E, the left valve 310 is open andthe right valve 310′ is closed. By providing the exact samefunctionality as a three-way valve, the examples illustrated in FIGS. 3Dand 3E may have some manufacturing advantages in resisting very highpressure operations due to the small size of each valve component.

Referring now to FIG. 3F, a two-way valve 330 suitable for draining lowpressure fluid from a tank is set forth. In this example, a port 332 isan inlet port within the housing 334. The inlet port 332 communicatesfluid to a drain port 336. The housing 334 has packing 340 that receivesthe actuator rod 342 coupled to the actuator 344. The rod 342 moves thevalve disk 350 toward or away from the valve seat 352. In FIG. 3F, thevalve seat 352 is spaced apart from the valve disk 350 and thus fluidflows between the inlet port 332 and the outlet port 336. As mentionedabove relative to FIG. 3C, the actuator 344 may be provided for eachvalve so that when two two-way valves replace a three-way valve,independent timing and control may be performed by the actuators foreach valve.

Referring now to FIGS. 3G and 3H, two valves 330, 330′ may be incommunication with a common actuator 344. In FIG. 3G, the left valve 330is closed and the right valve 330′ is open. The common components ofvalve 330 are primed in valve 330′. In FIG. 3H, the left valve is openand the right valve is closed. It should be noted that the valve disk350 is located between the valve port 332 and the valve seat 352. Whenclosed, the high pressure forces the valve disk 350 against the valveseat 352.

Referring now to FIG. 4A, a state table illustrating a transition of thevalves from a first state to a second state is set forth. The firststate “A” corresponds to the tank 40A injecting high pressure slurryinto the injection site 12 while high pressure clear fluid is an inputto the first tank 40A. At the same time, tank 40B is receiving lowpressure slurry from the slurry tank 30 and expelling clear fluid to thefluid tank 92. During the first state illustrated as “A” in FIG. 4A,valve 80A is open, valve 82A is closed, valve 82B is open and valve 80Bis closed. Three-way valve 140 is communicating fluid from port 140B toport 140C to the clear fluid tank 92. Valve 120 is communicating clearfluid from port 120A to 120B. Valve 110 is communicating clear fluidfrom port 110A to port 110B which ultimately communicates fluid throughvalve 120 and into tank 40A. Valve 124 is closed and valve 146 ispartially open.

In the table set forth in FIGS. 4A (and 4B), the bolded cells indicate achange in the valve state. Thus, only the bolded cells will be describedin the various states A1-A5. To begin the transition to state A′,multiple valve states are changed in sequence. State A1 is achieved bychanging the state of the three-way valve 110 to communicate fluid frominlet port 110A to outlet port 110C. The high pressure clear fluid fromthe pump 90 is diverted to the injection manifold 94. The high pressureclear fluid is no longer directed through the valve 120.

In state A2, the valve 150 is switched from communicating clear fluidfrom between port 150B and port 150C to communicating clear fluid frombetween port 150A and port 150C. The switching pressure differential ofthe valve 150 is reduced since the high pressure fluid is no longerbeing communicated to tank 40A through valve 120 due to the relief ofhigh pressure clear fluid flowing to the injection manifold 94 throughvalve 110.

In state A3, the depressurization of the tank 40A results in the checkvalves 80A, 82A and 82B switching states. That is, valve 80A is closed,valve 82A is open, and valve 82B is closed. Check valve 80B remainsclosed for this portion of the state change. The three-way valves 140and 120 are also changed in state. That is, valve 140 switches tocommunicate clear fluid from port 140A to port 140C. Three-way valve 120communicates fluid from port 120A to port 120C. Notice, the switching ofvalves 120 and 140 are performed when low pressures are at all theports.

In state A4, valve 124 is open which results in the check valve 80Bbeing open. By opening the valve 124, pipe 114 and thus the flow throughvalve 120 is increased. Port 110B also sees an increased pressure.

In state A5, valve 124 is closed and valve 110 is switched in state toterminate the diversion of high pressure clear fluid from the pump 90 tothe injection manifold 94. That is, valve 110 switches states so thatclear fluid is communicated between inlet port 110A and outlet port110B. The switching is performed while both ports 110A and 110B areunder a high pressure due to the diversion of high pressure clear fluidthrough valve 124.

In this example, states A1-A5 are switched 0.20, 0.3, 0.2, 0.25 and 0.20seconds respectively for a total switching state time of 1.15 seconds.Of course, the timing may be adjusted based on various conditions.

In state A′, a steady state of operation is achieved with check valve80A closed, check valve 82A open, check valve 82B closed, check valve80B open, and three-way valve 140 communicating low pressure fluid tothe tank 40A. Valve 120 is communicating high pressure clear fluid tothe tank 40B which results in high pressure slurry being injected intothe injection site 12 through the injection manifold 94. The valve 150is communicating fluid from tank 40A while valve 124 is closed. Valve146 is partially open. As will be described in more detail below, theswitching of the valves takes place based upon comparison from thesignals from the flow rate sensors 22 and 24. A comparison of the flowsignals from flow rate sensors 22 and 24 are compared. The flow ratesensor signals correspond to the volume of clear fluid entering one tankand leaving the other tank.

Referring now to FIG. 4B, operation of the injection system 10′ isillustrated. All of the states are the same except for the valve 150 hasbeen replaced by the valves 210A and 210B. In steady state A, valve 210Ais closed and valve 210B is open while the remaining valves are the sameas in FIG. 4A. In state A1, valves 210A and 210B remain closed and open,respectively. In step A2, valve 210A is open while valve 201B is closed.This allows the pressure in the first tank 40A to be depressurized orrelieved of pressure. In the remaining states A3-A5, valve 210A remainsopen while valve 210B is closed. Likewise, in steady state A′, valves210A and 210B are open and closed, respectively.

Referring now to FIG. 4C, a state diagram illustrating the operation orposition of the valves of FIG. 1E is set forth. In the slurry dischargestate, valve 80A is open, valve 82A is closed, valve 120′ is open, valve140′ is closed, valve 110 is open, valve 124 is closed and valve 210A isclosed. Valve 146 is partially closed so that the flow to the lowpressure clear fluid source is regulated. The state A illustrated aslurry discharge state in steady state operation. To transition throughthe process after slurry has been fully discharged as indicated by theoutput of the flow rate sensors, state A1 operates in the same mannerexcept for valve 110 has diverted flow to the manifold 94. The remainingstates are the same. In state A2, valve 80A is closed and valve 210A isopen. This allows the tank 40A to be depressurized.

In state A3, valves 82A, 120′ and 140′ are switched states so that valve82A is open, valve 120′ is closed and valve 140′ is open. In state A′,slurry begins to fill the tank. Slurry fills the tank until apredetermined amount of clear fluid is discharged as determined by theflow rate sensor 22. In state A′-1, the slurry discharge cycle isstarted by changing the states of valves 120′ to open and 140′ toclosed. This stops the slurry fill. In state A′-2, the valve 110 isopen. The system then continues in this state which corresponds to stateA where slurry is discharged. The process then starts over again.

Referring now to FIG. 5, a method of operating the system set forth inFIGS. 1A-1H is set forth. In step 510, the second volume 52 is filledwith slurry in tank 40A and a first volume 50 is filled with clearfluid. In step 512, a third volume 54 of the second tank is filled withclear fluid which is reduced by filling the fourth volume 56 with slurryfrom the low pressure slurry tank 30.

In step 514, the plurality of high pressure valves 110 and 120, inparticular, communicate high pressure clear fluid from the pump 90 andinto the pipe 60A. In response to communicating the high pressure clearfluid, step 516 moves the region 68A toward the end cap (downward inFIG. 1A) and high pressure slurry is communicated through the checkvalve 80A into the injection manifold 94 and injection.

In step 518, a fourth volume 56 is fluidically coupled to allow theslurry from the slurry pump 32 and slurry tank 30 to increase the fourthvolume. In response to increasing the fourth volume, clear fluid isreduced within the third volume which is displaced through the pipe 60Band is fluidically communicated through the valves 140 and 146 into theclear fluid tank 92. In step 522, the fluid flow rate of fluid from thetank 92 is measured by flow rate sensor 24. In step 524, a second fluidflow rate is determined from fluid flowing from the third volume 54 intothe tank 92. That is, the amount of clear fluid from the tank 40Bcommunicated to the clear fluid tank 92 is measured. In step 526, thecontroller 20 compares the first fluid flow rate and the second fluidflow rate. The flow rates correspond to the volumes entering and leavingtank 92. In step 528, the drain valve 146 is controlled in response tocomparing so that the flow through the valve 146 is increased ordecreased based upon the comparison. Ultimately, the amount of fluidflowing from the second tank may be controlled so that the amount ofslurry ready to be injected from the second tank 40B is available whenthe tank 40A is depleted of slurry. Preferably, while draining the tank40A of slurry, the amount of clear fluid may extend through the end capand just past the check valve 80A so that the check valve 80A closes ina clean fluid environment rather than in a slurry environment in step530. It is desirable to have the tank 40B and thus volume 56 at aprocess maximum before states A1-A5 of FIGS. 4A and 4B are performed.

In step 532, the plurality of clear fluid valves are controlled to causetank 40A to depressurize. This takes place in states A1 and A2 of FIGS.4A and 4B.

In step 534, the valves are changed in state in steps A3-A5 so that thesecond tank 40B is pressurized while tank 40A is depressurized and fillswith slurry. The switching process is described below.

Referring now to FIG. 6, the switching of the valves in the statesbetween state A and state A′ is illustrated in flowchart form. In step610, if the desired amount of clear fluid being removed from the secondtank 40B has been reached, the switching process begins. As mentionedabove, this corresponds to the flow rate or volume determined by theflow rate. Step 610 uses the comparison of step 526 to make thisdetermination. In step 612, the process of switching from state A to A′of FIGS. 4A and 4B is set forth. In step 614, high pressure clear fluidis redirected to the injection manifold through the three-way valve 110.In step 616, the first tank 40A is coupled to the clear fluid tankthrough valve 150. Check valve 80A closes in step 618 when the pressurein the tank 40A is reduced. The pressure reduction may be to or nearingto ambient pressure. In step 620, the state of the three-way valves 150and 120 are also changed as the valves are changed toward state A′.

In step 622, the pipe to the three-way valve 120 is pressurized byopening the valve 124. In step 624, and in response to the bypass valve124 being closed, valve 82B is closed and check valve 80B is open.Thereafter, in step 626 the state of the three-way valve 110 is changedto communicate high pressure clear fluid to tank 40B through thethree-way valve 120. In step 628, high pressure slurry is dischargedfrom tank 40B. In step 630, the check valve 82A is open to force clearfluid from the tank by displacing the clear fluid with low pressureslurry from the tank 15 and the slurry circulation pump 32. In step 632,clear fluid is communicated to the tank 92 through the valve 140 andvalve 146.

Referring now to FIG. 7A, a timing diagram for a multiple unit system isset forth. Each unit referred to in FIG. 7A comprises a pair of tanks.In FIG. 1, only two units are illustrated. However, as mentioned above,a plurality of units are set forth. In this example, five units, unit1-unit 5, are controlled having staggered starts of two seconds. Thatis, unit 1 starts at time 0 while unit 2 starts at 2 seconds, unit 3 at4 seconds, unit 4 at 6 seconds, and unit 5 at 8 seconds. A small dwelltime such as one-half second may be used in between each cycle for eachunit to accommodate slightly slower cycle rates or other variations.That is, the nominal cycle illustrated in FIG. 7A is 9.5 seconds with aone-half second dwell time therebetween. Unit 1 restarts after the dwelltime at 10 seconds, unit 2 at 12 seconds, unit 3 at 14 seconds, unit 4at 16 seconds and unit 5 at 18 seconds.

By staggering the start times, the amount of slurry injected during theprocess may be maintained and gradually increased and decreased comparedto a condition when the units would be in sync in terms of start times.Synchronized units may cause stress in the piping, valves and othercomponents. The number of units may equal the cycle time divided by theswitching time plus the dwell time which is multiplied by an integer. Inthis case, the cycle time is 10 seconds divided by the 2 second. Theresults are 5 units to obtain minimal flow variation. However integermultiples 10, 15 or 20 units (or more) may also be used to minimize flowvariation.

Referring now to FIG. 7B, a timing chart of a system is set forth usingsingle tank control such as the single tank of FIGS. 1E and 1F above.Single tank control with rapid slurry charging is set forth in FIG. 7B.In this example, each unit has a nominal five-second cycle time withfour-second slurry discharge and a one-second slurry fill. In thisexample, no dwell time is assumed. However, a dwell time may be used inoperation. The ratio of the slurry fill time to the slurry dischargetime is 1:5. That is, the discharging of slurry takes place 80% of thetime and slurry filling takes place 20% of the time. This is increasedover the embodiments including two tanks in which half the time the tankis charging while the other half of the time the tank is discharging.

Referring now to FIG. 8A, a slurry concentrate pressurizer configuration810 is illustrated. In this example, clear fluid is provided from aclear fluid source such as a reservoir 812 or tank. The reservoir 812 isin fluid communication with a low pressure pump 814. Clear fluid fromthe reservoir 812 enters a low pressure clear fluid manifold 816. Thelow pressure clear fluid manifold 816 is in communication with a trailer818. Because the systems are moved from wellsite to wellsite, mountingthe system components to a trailer is suitable. The trailer 818 may alsobe referred to as a “missile.” The trailer 818 has a portion of the lowpressure clear fluid manifold 820 and a portion of a high pressure clearfluid manifold 822 coupled thereto. The low pressure manifold 820 is influid communication with a plurality of high pressure clear fluid pumps830. The pumps 830 may be referred to as fracking pumps. The pluralityof pumps 830 may all be disposed on trailers 832 that may be hooked to asemi for easy transport from fracking site to fracking site. One or morepumps 830 may be disposed on each trailer 832. Each of the pumps 830draws low pressure fluid from the low pressure manifold 820 through aninlet pipe 840 and discharges high pressure clear fluid through anoutlet pipe 842. Only one each of pipes 840 and 842 are labeled. Thehigh pressure manifold 822 is in fluid communication with a static mixer852 though a two-way valve 850. The static mixer 852 is in communicationwith a well head 854. The high pressure clear fluid manifold 822 is influid communication with a slurry pressurizer 860 through a valve 862. Acontroller 864 is used to control the valves 850, 862 so that a portionof the high pressure clear fluid transmits through the valve 850 and aportion of the high pressure clear fluid is communicated to the slurrypressurizer 860. The controller 864 may be a programmable logiccontroller (PLC) that acts in response to one of more flow rate sensors866A, 866B or 866C. Of course, flow rate sensors 866A, 866B, 866C may bedisposed at various locations throughout the system 810 and generateflow signals that the controller 864 uses to control the system.

The slurry pressurizer 860 receives high pressure clear fluid andgenerates high pressure slurry through an output pipe 870 which is influid communication with the mixer 852. That is, the pipe 870 is influid communication with a point between the valve 850 and the mixer852. The mixer 852 forms a mixture of concentrated high pressure slurryfrom slurry pressurizer 860 and water from the valve 850.

The slurry pressurizer 860 also receives low pressure slurry from ablender unit 872 through a pipe 874. The blender unit 872 may alsoreceive additive from an additive tank 876 which is in fluidcommunication with a dosing pump 878. The dosing pump 878 communicatesthe fluid from the additive tank 876 into the blender unit 872. Theadditive within the additive tank 876 may comprise a gel or other typesof additive using in the fracking process. The slurry unit 872 may blendslurry, fluid and additives to form the low pressure slurry.

A centrifugal separator 880 receives low pressure fluid from the slurrypressurizer 860. The centrifugal separator 880 may separate any residualslurry from within the low pressure discharge and communicate the slurrymatter to the blender unit 872 through the pipe 882 for re-use. Theseparator 880 may also communicate clear fluid to the low pressuremanifold through pipe 884.

The blender unit 872 may also receive low pressure clear fluid from thelow pressure manifold 816 through a pipe 886. The low pressure clearfluid may be used to form the slurry.

In operation, the slurry pressurizer 860 may be disposed on a trailer890. The slurry pressurizer unit 860 may be one or more of the examplesset forth in FIG. 1A-1F. Both single or double tank slurry injectionunits may be used for the slurry pressurizer 860. In operation, thecontroller 864 controls the valve 850. The valve 850 may be used tocreate a differential pressure between a pipe 892 and pipe 870. Thedifferential pressure may be 75 psi or less. The valve 862 may beprecisely controlled so that the pressure thereacross is between 1 and20 psi. Valve 850 may be designed to not fully close. That is, apredetermined amount of flow through the valve 850 so that apredetermined amount of pressure differential is present across thevalve 850. For example, a 100 psi pressure differential may be used. Thevalve cannot fully close preventing accidental overpressurizing of thepumps and the piping. A suitable valve may be a leaky butterfly valve ora ball valve that is not allowed to physically close due to the geometrytherein.

Referring now to FIG. 8B, the static mixer 852 is illustrated in furtherdetail. The static mixer 852 has mixing elements 910 set forth thereinfor mixing the slurry and clear fluid communicated through the valve850. The mixer 852 blends the clear fluid and the concentrated slurryfrom the slurry pressurizer 860 that is received through the pipe 870.

In the example set forth in FIGS. 8A and 8B, the fracking pumps aresupplied by a single low pressure clear fluid line. The slurrypressurizer 860 draws low pressure clear fluid and returns low pressureclear fluid back to the clear fluid manifold 816. These connectionsminimize the amount of piping in a system. The centrifugal separator 880separates the slurry particulates from the low pressure clear fluid tonegligible amounts so that a minimum amount of particulates are in theclear fluid when entering the high pressure pumps. If various ones ofthe pumps 830 fail, the system can continue to pressurize slurry withminimal effect on the operation. The trailers 832 containing the pumps830 may easily be maneuvered to allow additional or replacement pumps tobe quickly connected to the trailer 818.

Because of the configuration, all the high pressure slurry mass isprovided by the trailer containing the slurry pressurizer 860. Theslurry pressurizer 860 may use vertical cylinders which keep the slurryin drive fluid from excessive mixing. As mentioned above, pistons mayalso be used within the various tanks to prevent mixing of the fluidstherein, particularly if the tanks are disposed at another angle otherthan vertical. The valves within the slurry pressurizer have a generallylow cycle rate of once every five to ten seconds versus six times persecond in a typical fracking pump. Valves designed for low velocitiesand materials that minimize erosion from concentrated slurry may beused.

Some slurry processes use 0.5 pounds of sand per gallon of high pressureclear fluid or about 0.75% concentration by weight. Highly dense slurrymay contain five pounds of sand per gallon. Based on the ratio, theslurry pressurizer 860 may only need to handle a flow of approximately10% of the total high pressure clear fluid flow to achieve a desiredslurry concentration downstream of the mixer 852. The additive tank 876may pass the additives through the slurry pressurizer 860 and thecapacity of the slurry pressurizer may be reduced. Because the slurrypressurizer 860 may provide a highly concentrated slurry due to thelater mixing within the mixer 852, the system may be referred to as aslurry concentrate pressurizer.

Referring now to FIG. 9, a method for operating the system of FIGS. 8Aand 8B is set forth. In step 930, clear fluid is received from a tank orreservoir at a low pressure pump. In step 932, the low pressure clearfluid is communicated to a low pressure manifold. The low pressure isnot high enough to operate the slurry pressurizer illustrated in FIG. 8.In step 934, a plurality of clear fluid pumps that are coupled to both ahigh pressure clear fluid manifold and a low pressure clear fluidmanifold increase the pressure of the low pressure clear fluid. In step936, the high pressure clear fluid generated at the plurality of clearfluid pumps is communicated to a high pressure clear fluid manifold.

In step 938, a portion of the high pressure clear fluid is communicatedfrom the high pressure clear fluid manifold through a mixer through afirst valve. In step 940, a portion of the high pressure clear fluidfrom the high pressure clear fluid manifold is communicated to a slurrypressurizer through a second valve. In step 942, the flow through thefirst valve and second valve is adjusted based on a flow rate or apressure monitored within the system.

In step 944, additives may be added to the low pressure slurry. Forexample, the additives may be a gel or other types of additives suitablefor improving the slurry fracking process. Step 944 is an optional step.Additives may be communicated to a slurry unit from a tank and a dosingpump.

In step 946, low pressure slurry is communicated to the slurrypressurizer. In step 948, high pressure slurry is communicated to themixer from the slurry pressurizer. In step 950, the low pressure clearfluid from the slurry pressurizer is communicated to a separator. Thelow pressure clear fluid is the result of the pressure transfer at theslurry pressurizer of high pressure from the high pressure clear fluidto the increase in pressure of the low pressure slurry to high pressureslurry. In step 952, the slurry residue may be extracted at a separator.The clear fluid may have a small amount of slurry therein. In step 954,the separated slurry at the extractor is communicated to the slurry unitand is later used for reinjecting to the slurry pressurizer. In step956, low pressure clear fluid is communicated to the low pressure clearfluid manifold from the separator. Should the clear fluid have anacceptably low amount of slurry particles therein, the separator may beeliminated from the system.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

What is claimed is:
 1. A slurry injection system comprising: a lowpressure clear fluid manifold; a high pressure clear fluid manifold; aplurality of clear fluid pumps receiving clear fluid from the lowpressure clear fluid manifold and pressurizing the clear fluid into highpressure clear fluid and communicating the high pressure clear fluidinto the high pressure clear fluid manifold; a blender unit having lowpressure slurry therein; a mixer in fluid communication with the highpressure clear fluid manifold through a first valve; and a slurrypressurizer in fluid communication with the high pressure clear fluidmanifold through a second valve, the mixer, the blender unit and the lowpressure clear fluid manifold, said slurry pressurizer forming highpressure slurry by pressurizing the low pressure slurry from the blenderunit using high pressure clear fluid from the high pressure clear fluidmanifold, said slurry pressurizer communicating high pressure slurry tothe mixer and communicating low pressure fluid to the low pressure clearfluid manifold; said mixer mixing the high pressure slurry and clearfluid from the first valve to form a mixture that is communicated to aslurry injection site.
 2. The slurry injection system as recited inclaim 1 wherein the first valve always at least partially opened.
 3. Theslurry injection system as recited in claim 1 wherein the first valvecomprises a two-way valve and wherein the second valve comprises atwo-way valve.
 4. The slurry injection system as recited in claim 1further comprising a separator fluidically coupling the slurrypressurizer and the low pressure clear fluid manifold, said separatorcommunicating slurry to the blender unit and clear fluid to the lowpressure clear fluid manifold.
 5. The slurry injection system as recitedin claim 1 further comprising a dosing pump communicating slurryadditive to the blender unit.
 6. The slurry injection system as recitedin claim 5 wherein the dosing pump communicates additive from anadditive tank to the blender unit.
 7. The slurry injection system asrecited in claim 1 wherein the mixer comprises a static mixer.
 8. Theslurry injection system as recited in claim 1 further comprising acontroller controlling the first valve and the second valve in responseto a flow signal corresponding to a high pressure clear fluid flow tothe slurry pressurizer.
 9. The slurry injection system as recited inclaim 1 further comprising a low pressure pump communicating clear fluidfrom a clear fluid source to the low pressure clear fluid manifold. 10.The slurry injection system as recited in claim 1 wherein the slurrypressurizer comprises a first elongated tank comprising a first endhaving a first volume and a second end having a second volume, saidfirst volume separated from the second volume; a first pipe having afirst end external to the first elongated tank receiving clear fluid anda second end coupled to the first volume; a plurality of slurry valvesfluidically coupled to the first elongated tank, said plurality ofslurry valves having a first state communicating high pressure slurryfrom the second volume to a slurry injection site and a second statecommunicating low pressure slurry into the second volume; and aplurality of clear fluid valves fluidically coupled to the firstelongated tank communicating high pressure clear fluid to the firstvolume in the first state and communicating low pressure clear fluidfrom the first volume in the second state.
 11. The slurry injectionsystem as recited in claim 1 wherein the slurry pressurizer furthercomprises a first elongated tank comprising a first end having a firstvolume and a second end having a second volume, said first volumeseparated from the second volume; a first pipe having a first endexternal to the first elongated tank receiving clear fluid and a secondend coupled to the first volume; a second elongated tank comprising afirst end having a third volume and a second end having a fourth volume,said third volume separated from the fourth volume; a second pipe havinga first end external to the second elongated tank receiving clear fluidand a second end within the third volume; a plurality of slurry valvesfluidically coupled to the first elongated tank and the second elongatedtank, said plurality of slurry valves having a first state communicatinghigh pressure slurry from the second volume to the slurry injection siteand communicating low pressure slurry to the fourth volume and a secondstate communicating low pressure slurry to the second volume and highpressure slurry from the fourth volume to a slurry injection site; and aplurality of clear fluid valves fluidically coupled to the firstelongated tank and the second elongated tank communicating high pressureclear fluid to the first volume and communicating low pressure clearfluid from the third volume in a first state and communicating lowpressure clear fluid to the first volume and high pressure clear fluidto the third volume in a second state.
 12. A method of operating aslurry injection system comprising a low pressure clear fluid manifold,a high pressure clear fluid manifold, a plurality of clear fluid pumps,a blender unit, a mixer, and a slurry pressurizer comprising: receivingclear fluid from the low pressure clear fluid manifold at the pluralityof clear fluid pumps; pressurizing the clear fluid into high pressureclear fluid at the plurality of clear fluid pumps; communicating thehigh pressure clear fluid into the high pressure clear fluid manifoldfrom the plurality of clear fluid pumps; communicating high pressureclear fluid from the high pressure clear fluid manifold to the mixerthrough a first valve; communicating the high pressure clear fluid fromthe high pressure clear fluid manifold to the slurry pressurizer througha second valve; pressurizing, by the slurry pressurizer, low pressureslurry from the blender unit using high pressure clear fluid from thehigh pressure clear fluid manifold to form high pressure slurry;communicating low pressure fluid from the slurry pressurizer to the lowpressure clear fluid manifold; blending, at a mixer, the high pressureslurry with high pressure clear fluid from the second valve to form aslurry mixture; and communicating the mixture to an injection site. 13.The method as recited in claim 12, further comprising at least partiallyopening the first valve prior to blending.
 14. The method as recited inclaim 12 further comprising coupling the slurry pressurizer and the lowpressure clear fluid manifold through a separator and communicating,through the separator, slurry to the blender unit and clear fluid to thelow pressure clear fluid manifold.
 15. The method as recited in claim 12further comprising communicating slurry additive to the blender unitfrom a dosing valve.
 16. The method as recited in claim 12 furthercomprising controlling the first valve and the second valve in responseto a flow signal corresponding to a high pressure clear fluid flow tothe slurry pressurizer.
 17. The method as recited in claim 12 furthercomprising communicating clear fluid from a clear fluid source to thelow pressure clear fluid manifold using a low pressure pump.